Canon made the smart move of supporting legacy glass quite well, with most lenses performing as good or better on mirrorless bodies than they did on DSLRs. It gave up some potential revenue, but made the barrier of switching to other brands (most notably Sony) much bigger.
There are a handful of reasons some photographers still want DSLRs. The two I've heard most are battery life and physical size/layout. Mirrorless are improving with battery performance, and it seems most photographer's are willing to carry an extra battery if needed. Still, certain photographers or situations desire maximum endurance.
There are also some photographers that like larger cameras. Given the majority of the market seems to want smaller and lighter, I doubt we are going to see mirrorless units get bigger. If you favor the ergonomics of a larger camera, a DSLR is going to be worth investigating.
Other early issues, like EVFs vs optical viewfinders, seem to be going away with the advancement of tech.
Its hard to argue with that, at least if you are a serious amateur or pro. Point and shoot fans may not have as much to look forward too!